<template>
  <div class="header">
    <router-link tag="div"
                 to="/"
                 class="header-abs"
                 v-show="showAbs">
      <span class="iconfont back-icon">&#xe624;</span>
    </router-link>
    <div class="header-fixed"
         v-show="!showAbs"
         :style="opacityStyle">
      <router-link to="/">
        <div class="iconfont back-icon">&#xe624;</div>
      </router-link>
      景点详情
    </div>
  </div>
</template>
<script>
export default {
  data () {
    return {
      showAbs: true,
      opacityStyle: {
        opacity: 0
      }
    }
  },
  methods: {
    handleScroll () {
      let top = document.documentElement.scrollTop
      if (top > 50) {
        let opacity = top / 120
        opacity = opacity > 1 ? 1 : opacity
        this.opacityStyle = { opacity }
        this.showAbs = false
      } else {
        this.showAbs = true
      }
    }
  },
  // 页面展示时
  activated () {
    window.addEventListener('scroll', this.handleScroll)
  },
  // 页面被隐藏时
  deactivated () {
    window.removeEventListener('scroll', this.handleScroll)
  }
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.header
  .header-abs
    position: absolute
    left: 0.2rem
    top: 0.2rem
    width: 0.7rem
    height: 0.7rem
    line-height: 0.7rem
    font-size: 0.4rem
    text-align: center
    background: rgba(0, 0, 0, 0.5)
    color: #fff
    border-radius: 50%
  .header-fixed
    position: fixed
    top: 0
    left: 0
    right: 0
    height: $headerHeight
    line-height: $headerHeight
    background: $bgColor
    color: #fff
    text-align: center
    .back-icon
      position: absolute
      left: 0
      top: 0
      width: 0.64rem
      font-size: 0.4rem
      text-align: center
      color: #fff
</style>
